2,3-dihydro-6-nitroimidazo[2,1-b]oxazole compounds represented by general formula (1) shown below, optically active isomers thereof, and pharmacologically acceptable salts thereof (all of which are simply referred to as “oxazole compounds” below) are known to exhibit excellent bactericidal effects against mycobacterium tuberculosis, multidrug-resistant tubercle bacilli, and atypical acid-fast bacteria (see Japanese Unexamined Patent Publication No. 2004-149527 and WO 2005-042542): general formula (1):

wherein R1 represents a hydrogen atom or C1-6 alkyl group; n represents an integer from 0 to 6; and R2 represents any of the groups represented by general formulae (A) to (F) below:
groups represented by general formula (A):

wherein R3 represents any of the groups (1) to (6) shown below:
(1) phenoxy groups, optionally substituted on the phenyl ring with one or more members selected from the group consisting of halogen atoms, halo-substituted or unsubstituted C1-6 alkyl groups, and halo-substituted or unsubstituted C1-6 alkoxy groups;
(2) phenyl C1-6 alkoxy groups, optionally substituted on the phenyl ring with one or more members selected from the group consisting of halogen atoms, halo-substituted or unsubstituted C1-6 alkyl groups, and halo-substituted or unsubstituted C1-6 alkoxy groups;
(3) —NR4R5 groups, wherein R4 represents a C1-6 alkyl group, and R5 represents a phenyl group, optionally substituted on the phenyl ring with one or more members selected from the group consisting of halogen atoms, halo-substituted or unsubstituted C1-6 alkyl groups, and halo-substituted or unsubstituted C1-6 alkoxy groups;
(4) phenyl C1-6 alkyl groups, optionally substituted on the phenyl ring with one or more members selected from the group consisting of halogen atoms, halo-substituted or unsubstituted C1-6 alkyl groups, and halo-substituted or unsubstituted C1-6 alkoxy groups;
(5) phenoxy C1-6 alkyl groups, optionally substituted on the phenyl ring with one or more members selected from the group consisting of halogen atoms, halo-substituted or unsubstituted alkyl groups, and halo-substituted or unsubstituted C1-6 alkoxy groups; and
(6) benzofuryl C1-6 alkyl groups, optionally substituted on the benzofuran ring with one or more members selected from the group consisting of halogen atoms, halo-substituted or unsubstituted alkyl groups, and halo-substituted or unsubstituted C1-6 alkoxy groups;
groups represented by general formula (B):

wherein R6 represents a phenyl group, optionally substituted on the phenyl ring with one or more members selected from the group consisting of halogen atoms, halo-substituted or unsubstituted C1-6 alkyl groups, and halo-substituted or unsubstituted C1-6 alkoxy groups;
groups represented by general formula (C):

wherein R7 represents a phenyl C2-10 alkenyl group, optionally substituted on the phenyl ring with one or more members selected from the group consisting of halogen atoms, halo-substituted or unsubstituted C1-6 alkyl groups, and halo-substituted or unsubstituted C1-6 alkoxy groups, or represents a biphenyl C1-6 alkyl group, optionally substituted on one or both phenyl rings with one or more members selected from the group consisting of halogen atoms, halo-substituted or unsubstituted C1-6 alkyl groups, and halo-substituted or unsubstituted C1-6 alkoxy groups;
groups represented by general formula (D):

wherein R8 represents a phenyl C1-6 alkyl group, optionally substituted on the phenyl ring with one or more members selected from the group consisting of halogen atoms, halo-substituted or unsubstituted C1-6 alkyl groups, and halo-substituted or unsubstituted C1-6 alkoxy groups;
groups represented by general formula (E):

wherein R8 is the same as above; and
groups represented by general formula (F):

wherein R8 is the same as above.
The oxazole compounds represented by general formula (1) above have low solubilities in water, and hence there is a demand for improvements in their solubilities.